Generally, a vehicular suspension system is an apparatus for connecting a wheel to a vehicular body. The suspension system consists of a spring that absorbs impact from a road surface, a shock absorber that adjusts an action of the spring, an arm or link that controls an operation of the wheel, and a stabilizer that prevents rolling of a vehicle.
The aforementioned vehicular suspension system is an important apparatus for promoting ride comfort and driving stability, and mainly performs the functions of suppressing or rapidly reducing vibrations transmitted from a vehicular wheel while stably supporting the vehicular body from the vehicular wheel in a stable manner.
In such a suspension system, a lower arm is used to perform the functions of connecting the vehicular wheel to the vehicular body and supporting the vehicular wheel.
FIG. 8 is a perspective view of a lower arm according to a prior art technology.
As shown in FIG. 8, a lower arm 1 according to a prior art technology is configured in a structure where a vehicular body mounting bush 10 (commonly referred to as an “A bush” in the art), a damping joint 20 (commonly referred to as a “G bush” in the art), and a ball joint 30 are coupled to three end portions.
In this regard, the vehicular body mounting bush 10 and the damping joint 20 are coupled to a vehicular body frame 2 through respective assembly bolts 41 and 42, and the ball joint 30 is coupled to a knuckle of the vehicular wheel to support the vehicular wheel together with an upper arm.
The damping joint 20 simultaneously prevents, among random excitations transmitted from the outside of a vehicle, the following: an impact harshness phenomenon which is a temporary vibration generated after an impact sound when a tire of the vehicle passes over a protrusion of a road surface while the vehicle is being driven; a shimmy phenomenon in which the steering wheel of the vehicle that is turning shakes left and right in the turning direction; and a judder phenomenon in which noise or vibration is generated in the steering wheel or a dash panel when a braking force is applied while the vehicle is driven at a high speed.
FIG. 9 is a sectional view of a ball joint according to a prior art technology.
As shown in FIG. 9, the ball joint 30 according to prior art includes a housing 31, a bearing 32, a cap 33, a ball stud 34, and a dust cover 35.
The housing 31 is generally formed of a metal material for maintaining a strength of a ball bearing, and upper and lower ends of the housing are open. A deformed portion 38 is formed integrally at the lower end of the housing 31.
The bearing 32 is mounted inside the housing 31 and is generally made of a plastic material. An upper end of the bearing 32 is open, and a space is formed in the bearing 32 such that a ball 39 of the ball stud 34 is inserted in the space.
The cap 33 supports a lower portion of the bearing 32 and closes the lower end of the housing 31. That is, the bearing 32 is positioned inside the housing 31 and the lower end of the housing 31 is closed by the cap 33. At this time, the deformed portion 38 of the housing 31 protrudes below the cap 33. To assemble the cap 33 to the housing 31, the deformed portion 38 is caulked toward the cap 33.
The ball 39, which is inserted into and pivoted in the space of the bearing 32, is formed at one end of the ball stud 34. Screw threads 37 are formed at the opposite end of the ball stud 34.
The dust cover 35 prevents foreign matters from entering between the bearing 32 and the ball 39. The dust cover 35 is generally made of an elastic material such as rubber. The dust cover 35 is inserted to the ball stud 34 and is mounted to an upper portion of the housing 31. Further, the dust cover 35 includes fixing members 36 which fix upper and lower ends of the dust cover 35.
However, in the above-described ball joint of the prior art, the housing is made of a metal material by casting and had to be used by polishing the surfaces of the housing. Further, additional parts for assembling the ball joint must be used and thus the weight of the ball joint was increased. Accordingly, the weight of a vehicle in which several to dozens of ball joints are used is increased, thereby reducing the fuel efficiency of the vehicle. In addition, the prior art ball joint was required to undergo an additional assembly process of press-fitting the ball joint to the lower arm. Thus, there have been problems due to an increased manufacturing time and manufacturing costs.